There is an industry push toward reducing power consumption in computer systems. For example, some government bodies require energy compliant computing systems. The need for reducing the power consumption of computers is especially keen for battery-operated mobile computing systems, such as laptops or notebook personal computers. Because the power source of mobile computers accounts for a significant percentage of the bulk and weight of the device, attempts have been made since the advent of laptops to reduce their power consumption.
In addition, there is an ever-constant push in the computing industry to deliver computing systems having increased computing performance. Mobile computers, such as laptop and notebook computers, are not immune to the ever-constant push to deliver higher performing systems. In mobile computers, such as a laptop or notebook computer, there is also an ever constant push to manage power to maintain or increase the time between battery rechargings. In mobile computing environments, power management is also important since it is related to the amount of heat generated. Generally, the higher the amount of power consumed, the more heat that will be generated. In mobile computers, the components are packed into a smaller housing so any heat generated is concentrated within the smaller housing and must be managed more effectively to prevent device or component failure.
Power consumption of a semiconductor device or component includes not only the active power used by a component or device, but also includes the leakage power consumed by a component or device. Leakage power results from leakage current. Leakage current is inherent in devices or components that include transistors. Leakage current is current that conducts through a transistor even when the transistor is supposed to be off. In most circuit configurations, leakage current is undesirable because it consumes power without producing useful work. Leakage power consumption is inherent in semiconductor physics and is a product of the design methods used to create high speed processors. Leakage power consumption is caused by a voltage gradient across a junction within a semiconductor chip that causes current flow.
Currently, high performance devices are experiencing larger leakage currents as a percentage of total current consumption because of the greater number of transistors, with each transistor having a larger leakage current. The development of high performance devices or components, such as microprocessors, has lead to increased leakage power consumption because higher frequency devices employ smaller transistors in larger numbers than ever before. The smaller the transistor channel length and oxide thickness, the greater the leakage power consumption.